1. Field of the Invention
This invention relates to an image processing apparatus, such as an original reading apparatus, a copier, a facsimile apparatus or the like, having an original feed device.
2. Description of the Related Art
Heretofore, image processing apparatuses have been used which have an original feed function to feed an original onto a platen glass, and a so-called AE (automatic density adjustment) function to automatically detect the density of an image of the original and to adjust the density of a copy to a proper density by changing the amount of light of an exposure lamp in an optical scanning system. An image density detection means for the AE function in such an image processing apparatus is provided either in (i) an optical scanning system or in (ii) an original feed system.
In an apparatus (i) having an image density detection means for the AE function in an optical scanning system, after an original has been fed onto a platen glass and stopped, the original is prescanned by the optical scanning system to sample AE data, and the amount of light of an exposure lamp is determined according to the sampled AE data. Subsequently, scanning for image reading is performed in accordance with the amount of light of the exposure lamp determined.
In an apparatus (ii) having an image density detection means for the AE function in an original feed system, the image density detection means is disposed in an original feed path, and the density of an image of an original is detected while feeding the original.
However, the above-described conventional apparatuses having only one image density detection means for the AE function have, for example, the following disadvantages. In the apparatus (i) having the image density detection means for the AE function in the optical scanning system, in order to perform stable image density detection, prescanning of the optical scanning system for AE data to be sampled is needed before scanning (image scanning) for image reading. Hence, the number of operations for every original increases, and processing time is increased. As a result, the copying efficiency of the apparatus is substantially decreased particularly when performing image processing for a large number of originals, though the same holds true even for a single original.
In the apparatus (ii) having the image density detection means for the AE function in the original feed system, since the image density detection means is provided in an original feed unit, the AE function cannot be used when a copying operation is performed without using the original feed unit. Furthermore, the image density detection level becomes unstable due, for example, to stain by paper powder during a long period in the original feed operation. As a result, a proper amount of light of the exposure lamp cannot be obtained, and the AE function does not properly function.